struct Owner(i32);

impl Owner {
    fn add_one<'a>(&'a mut self)  { self.0 += 1 }
    fn print<'a>(&'a self) { println!("{}", self.0) }
}

fn main() {
    let mut owner = Owner(5);
    owner.print();

    owner.add_one();
    owner.print();
}